Dr. Martin P. Paulus, a professor of psychiatry at the University of California San Diego, and an author of the study, offered this theory as to why something without calories can lead to weight gain:

“Your senses tell you there’s something sweet that you’re tasting, but your brain tells you, ‘Actually, it’s not as much of a reward as I expected,‘ he explained. “So you chase that no-calorie soda with something more caloric, like a salty snack. The sweet taste could also trigger your body to produce insulin, which blocks your ability to burn fat.”